An armature of a high-powered generator or alternator is comprised of a set of bars, called armature bars, which obtain extremely high electrical current densities, and therefore, high temperatures. These armature bars are generally cooled with a coolant circulating inside the bars. The coolant is traditionally water, often deionized, but other coolants can be used in liquid or gaseous form, such as oil, hydrogen, nitrogen, oxygen, argon, helium, krupton, methane, air, or another fluid.
A fluid-cooled armature bar is comprised of a plurality of rectangular, solid, conductor strands and a plurality of hollow conductor strands. These solid conductor strands and hollow conductor strands are arranged to form a bar. The rectangular conductor strands are generally arranged or stacked in columns or rows, with the hollow conductor strands interspaced among the solid conductor strands. The hollow conductor strands each have an internal duct for conducting coolant through the armature bar.
Each armature bar extremity ends at a cooling fluid box which acts as a reservoir for the cooling fluid, and which links with other elements of the cooling circuit. A cooling fluid box can also be referred to as a “hydraulic clip”, “clip”, “header”, “end fitting”, “water box”, or another variation of these terms. The connection between each bar and its associated cooling fluid box is intended to be impervious to prevent the cooling fluid from leaking between the outside and inside of the cooling fluid box since leaks can result in isolation defects and corrosion problems.
To make the junction between the armature bar end and the cooling fluid box impervious to cooling fluid leaks, the end of the armature bar is brazed to the cooling fluid box. At one open end, the cooling fluid box encloses the ends of the conductor strands of one end of the armature bar, and a braze alloy bonds the end of each conductor strand to the neighboring conductor strand(s) and/or to the neighboring surface(s) of the cooling fluid box. The brazed joints between the adjacent conductor strands, and the brazed joints between the conductor strands and the cooling fluid box should retain electrical integrity while providing a fluid-tight barrier.
To braze, the hollow and solid conductor strand ends are assembled in stacks and positioned within the cooling fluid box. Braze alloy is then melted and wicked into voids or gaps during induction heating. The braze alloy spreads, bridging from surface to surface to fill the gaps through capillary action, which is increasingly effective as the distance between surfaces (i.e. the breadth of the gaps) decreases. For instance, a gap distance of 0.001 inches (≈0.0025 cm) to 0.003 inches (≈0.0076 cm) allows for an effective brazing and a strong brazed joint. With a gap distance of 0.003 inches (≈0.0076 cm) to 0.005 inches (≈0.0127 cm), the braze alloy can still properly bridge the gaps, but with less reliability than with a gap distance of 0.001 inches (≈0.0025 cm) to 0.003 inches (≈0.0076 cm). A gap distance of more than 0.005 inches (≈0.0127 cm) can result in a weak braze joint, as the braze alloy will likely not bridge the gaps well to fill all the spaces. With the importance of providing a leak free, fluid-tight, electrically intact joint, it is beneficial to assemble the conductor strands to be jointed to the cooling fluid box with minimal space between each conductor strand, and between the strands and the cooling fluid box, so that a strong braze can be achieved.
Because the conductor strands are not perfectly rectangular, but rather are rounded to some degree on the corners, when the strands are grouped together to form a bar, large gaps can remain where the corners of four conductor strands meet. To lessen the gaps, it is beneficial to secure the conductor strands in place tightly where the conductor strands will be brazed to the cooling fluid box. A tight fit also reduces the chance of movement during brazing. Movement of the conductor strands with respect to each other, or with respect to the cooling fluid box during brazing can also cause less durable and less structurally sound joints that are less impervious to leaking.
Achieving this tight fit to avoid a weak braze joint can be difficult, especially while simultaneously establishing proper alignment and position of the conductor strands in the cooling fluid box. To slide the cooling fluid box around the armature bar in preparation for brazing, there must be adequate physical clearance between the interior opening of the cooling fluid box and the perimeter of the armature bar. Providing this clearance reduces the tightness of the fit. Columns of conductor strands making up the armature bar do not squeeze tightly together to reduce or eliminate gaps. Therefore, in designing sufficient clearance, large gap distances are inherently designed into the assembly as well. These gap distances exceed 0.005 inches (≈0.0127 cm), which do not fill well by capillary action during brazing.
On the other hand, to achieve a tighter fit, it can be beneficial to dimension the armature bar larger than the opening of the cooling fluid box into which the armature bar will be fit. However, pressing the armature bar into an area smaller than the armature bar presents difficulty. Under present methods of assembling the armature bar to be brazed within the cooling fluid box, a tight fit of the armature bar and its individual conductor strands inside the cooling fluid box is difficult to achieve, allowing large gaps that are difficult to fill during brazing. The brazed joints, as a result, are not as strong, not as durable, and not as impervious to leaking.
It would be advantageous to provide an easier assembly method and an apparatus to firmly secure the conductor strands in position during the brazing procedure. It would also be advantageous to provide an easier assembly method and an apparatus to reduce the gap sizes between the strands, and between the strands and the cooling fluid box.